/*
 * Copyright (C) 2016 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.graph;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.base.Function;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;
import com.google.errorprone.annotations.Immutable;

/**
 * A {@link ValueGraph} whose elements and structural relationships will never change. Instances of
 * this class may be obtained with {@link #copyOf(ValueGraph)}.
 *
 * <p>
 * See the Guava User's Guide's <a href=
 * "https://github.com/google/guava/wiki/GraphsExplained#immutable-implementations">discussion of
 * the {@code Immutable*} types</a> for more information on the properties and guarantees provided
 * by this class.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @param <V> Value parameter type
 * @since 20.0
 */
@Beta
@Immutable(containerOf = {"N", "V"})
@SuppressWarnings("Immutable") // Extends ConfigurableValueGraph but uses ImmutableMaps.
public final class ImmutableValueGraph<N, V> extends ConfigurableValueGraph<N, V> {

    private ImmutableValueGraph(ValueGraph<N, V> graph) {
        super(ValueGraphBuilder.from(graph), getNodeConnections(graph), graph.edges().size());
    }

    /** Returns an immutable copy of {@code graph}. */
    public static <N, V> ImmutableValueGraph<N, V> copyOf(ValueGraph<N, V> graph) {
        return (graph instanceof ImmutableValueGraph) ? (ImmutableValueGraph<N, V>) graph
                : new ImmutableValueGraph<N, V>(graph);
    }

    /**
     * Simply returns its argument.
     *
     * @deprecated no need to use this
     */
    @Deprecated
    public static <N, V> ImmutableValueGraph<N, V> copyOf(ImmutableValueGraph<N, V> graph) {
        return checkNotNull(graph);
    }

    @Override
    public ImmutableGraph<N> asGraph() {
        return new ImmutableGraph<N>(this); // safe because the view is effectively immutable
    }

    private static <N, V> ImmutableMap<N, GraphConnections<N, V>> getNodeConnections(ValueGraph<N, V> graph) {
        // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will
        // have
        // whatever ordering the graph's nodes do, so ImmutableSortedMap is unnecessary even if the
        // input nodes are sorted.
        ImmutableMap.Builder<N, GraphConnections<N, V>> nodeConnections = ImmutableMap.builder();
        for (N node : graph.nodes()) {
            nodeConnections.put(node, connectionsOf(graph, node));
        }
        return nodeConnections.build();
    }

    private static <N, V> GraphConnections<N, V> connectionsOf(final ValueGraph<N, V> graph, final N node) {
        Function<N, V> successorNodeToValueFn = new Function<N, V>() {
            @Override
            public V apply(N successorNode) {
                return graph.edgeValue(node, successorNode);
            }
        };
        return graph.isDirected()
                ? DirectedGraphConnections.ofImmutable(graph.predecessors(node),
                        Maps.asMap(graph.successors(node), successorNodeToValueFn))
                : UndirectedGraphConnections.ofImmutable(Maps.asMap(graph.adjacentNodes(node), successorNodeToValueFn));
    }
}
